The word 'swollen' is the past participle of the verb 'swell,' which originates from the Proto-Germanic root swellaną, meaning "to swell up." This root is part of a wider Indo-European family of words related to bulging or rounding out. The addition of the '-en' suffix follows a classic Germanic pattern for forming adjectives from strong verbs, indicating a state resulting from the action. Thus, the literal sense of "having been caused to grow larger" evolved into the modern medical and descriptive meanings of being enlarged due to internal pressure, fluid, or growth.

Structure: swell + en swell: From Old English swellan, meaning "to grow or make larger." It is a Germanic root. en: A suffix of Old English origin used to form past participles of strong verbs (like broken, spoken) and adjectives from nouns (like wooden, golden).